decompression

noun

de·​com·​pres·​sion -ˈpresh-ən 

: the act or process of releasing from pressure or compression: as

a

: reduction of pressure:

(1)

: the decrease of ambient air pressure experienced in an air lock on return to atmospheric pressure after a period of breathing compressed air (as in a diving bell or caisson) or experienced in ascent to a great altitude without a pressure suit or pressurized cabin

(2)

: the decrease of water pressure experienced by a diver when ascending rapidly

b

: an operation or technique used to relieve pressure upon an organ (as in fractures of the skull or spine) or within a hollow organ (as in intestinal obstruction)